Selecting the proper size of heater(s) to match your commercial needs is of the outmost importance. Please consult with the Noritz commercial team for any inquires or concerns ragarding sizing call at (866) 766-7489 (option 3) or email at We will be more than happy to assist you.


The FAST Four Factors for Commercial Sizing.

  • Fixtures: What are the hot water demands on the location? An accurate count on the type and number of hot water fixtures are required for accurate sizing. Examples include: number of showers, lavatory sinks, dishwashers, washing machines, and compartment sinks.
  • Application Type: What type of commercial application is it going to be? Examples include : restaurant, hotel, apartment, Laundromat, or gym. Each different type of application will have very different hot water requirements.
  • Special use fixtures:Special use fixtures are the fixtures which have abnormal or metered water demands. Examples include : Commercial dish machines, commercial extractors (washinh machines), automatic car washes, and custom showers (multiple body sprays). For these particular types of fixtures, it is very strongly recommended to have the make and model available. If not available, the size of the associated hot water line will be needed.
  • Temperature rise: Temperature rise is the number of degrees (Fahrenheit/Celsius) required to raise the water from the ground water temperature to set the point temperature.


    Temperature rise = (Set Point Temperature) - (Ground Water Temperature)

    Ground water temperature - The incoming water temperature of the local water supply (municipal or well). For sizing purposes, the incoming water temperature should be estimated for the coldest time of the year.

    Set Point Temperature - The set point temperature is the temperature that the heater will be set. The heater should be set at the temperature required to meet the hot water demand. If multiple different hot water temperatures are required, the highest required temperature should be used.

Sizing and "Peak demand"

Sizing a water heating system utilizing Noritz commercial water heaters requires an estimation of peak demand. Peak demand is defined as the highest amount of hot water being used simultaneously. This is not to be confused with the sizing of a peak load. Peak load refers to the maximum amount of hot water over a given time period (usually a 1-3 hour block) used for sizing commercial storage. Peak demand is calculated from the FAST four factors. Please call our commercial team at (866) 766-7489, with this information and we will be glad to assist you in obtaining the correct heater(s) for the job.

(For peak flow rates in shaded areas, contact Noritz for proper settings.)